One of Cooper's costars, "Nashville" star Eric Close, opened up about Bradley's preparations for the part with E!. "He put on like 40 pounds," says Close. "He's really been working hard. He looks great. He's really taken on this character ... He really takes this story personally and wants to do an honorable job for Chris' memory and for his family."

The movie, directed by Clint Eastwood, is set to hit theaters in 2015.

Cooper is hardly the first actor to drastically change his physique for a movie role. Check out the gallery above to see more crazy transformations!